WO1999015915A1 - Excitation optimisee du deplacement chimique en imagerie par resonance magnetique (irm) - Google Patents

Excitation optimisee du deplacement chimique en imagerie par resonance magnetique (irm) Download PDF

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Publication number
WO1999015915A1
WO1999015915A1 PCT/US1998/020100 US9820100W WO9915915A1 WO 1999015915 A1 WO1999015915 A1 WO 1999015915A1 US 9820100 W US9820100 W US 9820100W WO 9915915 A1 WO9915915 A1 WO 9915915A1
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Prior art keywords
pulse
pulse sequence
magnetization
åulse
inte
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Application number
PCT/US1998/020100
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English (en)
Inventor
Jeffrey L. Duerk
Michael Wendt
Jonathan S. Lewin
Dee H. Wu
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Case Western Reserve University
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Publication date
Application filed by Case Western Reserve University filed Critical Case Western Reserve University
Priority to US09/509,325 priority Critical patent/US6404198B1/en
Priority to AU96665/98A priority patent/AU9666598A/en
Publication of WO1999015915A1 publication Critical patent/WO1999015915A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/446—Multifrequency selective RF pulses, e.g. multinuclear acquisition mode
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/4828—Resolving the MR signals of different chemical species, e.g. water-fat imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/44—Arrangements or instruments for measuring magnetic variables involving magnetic resonance using nuclear magnetic resonance [NMR]
    • G01R33/48—NMR imaging systems
    • G01R33/483—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy
    • G01R33/4833—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices
    • G01R33/4835—NMR imaging systems with selection of signals or spectra from particular regions of the volume, e.g. in vivo spectroscopy using spatially selective excitation of the volume of interest, e.g. selecting non-orthogonal or inclined slices of multiple slices

Definitions

  • the present invention relates generally to the field of magnetic resonance imaging (MRI). More particularly, the present invention relates to the field of MRI chemical-shift excitation.
  • MRI magnetic resonance imaging
  • a subject such as a human body is placed in a static magnetic field such that selected nuclear magnetic dipoles of the subject preferentially align with the magnetic field.
  • the MRI system then applies radio frequency (RF) pulsed magnetic fields to cause magnetic resonance of the preferentially aligned dipoles and detects RF magnetic resonance (MR) signals from the resonating dipoles for reconstruction into an image representation.
  • RF radio frequency
  • MR RF magnetic resonance
  • the MRI system typically scans the region to be imaged by applying RF pulse sequences to the subject while imposing time-varying magnetic field gradients with the static magnetic field.
  • the hydrogen protons from water are preferably detected as most soft tissues are composed of greater than approximately eighty percent water.
  • fat is also largely composed of hydrogen protons and may therefore appear as an unwanted or unnecessary component in many hydrogen MR images.
  • a variety of methods have been developed to help eliminate the effect of fat magnetization from hydrogen MR images and thereby improve the contrast between normal and pathologic tissue in a variety of anatomic locations such as, for example, the liver and pancreas, the orbits, the breast, bone marrow, and the coronary arteries.
  • Water excitation methods apply an RF pulse sequence to tip water magnetization and not fat magnetization for detection.
  • Fat suppression methods apply an RF pulse sequence to tip fat magnetization and not water magnetization, eliminate the fat magnetization, and then excite the water magnetization for detection. Such methods are able to tip water and fat magnetization in a selective manner because of the chemical shift difference in resonant frequency between water protons and protons in the methylene (-CH 2 ) groups of fat molecules.
  • ⁇ is the Larmor frequency of the nuclei of interest
  • ⁇ is the gyromagnetic ratio of the nuclei of interest
  • Bo is the applied static magnetic field.
  • One common fat suppression method applies binomial sets of RF pulses at specific amplitudes and specific interpulse intervals to tip fat magnetization into the transverse or detection plane while restoring water magnetization to the longitudinal axis.
  • the fat magnetization may be spoiled or destroyed.
  • a selective RF pulse may then be applied to tip the remaining longitudinal magnetization into the detection plane.
  • Exemplary prior art binomial RF pulse sequences include l-(-l), l-(-2)-l,
  • a second RF pulse in the l-(-l) sequence tips both water magnetization 11 and fat magnetization 12 by approximately -45°, restoring water magnetization 11 to the z-axis while tipping fat magnetization 12 into the detection plane as illustrated in Figure ID.
  • Fat magnetization 12 is then spoiled by a magnetic field gradient pulse as illustrated in Figure IE, and water magnetization 11 may then be tipped from the z-axis into the detection plane by a selective RF pulse.
  • Adding more RF pulses in a binomial sequence helps improve the spectral width of the saturation in an inhomogeneous magnetic field.
  • a binomial 1-3-3-1 RF pulse sequence may be used for fat suppression.
  • the effectiveness of binomial RF pulse sequences in suppressing fat may be compromised in relatively lower magnetic fields as the relatively longer interpulse intervals together with the reduced relaxation time Tl for fat in the lower magnetic field allow significant fat magnetization regrowth. Relatively longer interpulse intervals also allow greater water magnetization decay as determined by the relaxation time T2 for water.
  • FIG. 2 A water magnetization 21 and fat magnetization 22 are initially aligned with the static magnetic field Bo along the z-axis at equilibrium.
  • An inverting RF pulse tips both water magnetization 21 and fat magnetization 22 by approximately 180° as illustrated in Figure 2B.
  • fat magnetization regrowth 23 effectively cancels inverted fat magnetization 22 as illustrated in Figure 2C.
  • Water magnetization 21 may then be tipped into the detection plane by a selective RF pulse.
  • Inversion methods for fat suppression may also suppress the magnetization from tissues having a relaxation time Tl comparable to that of fat and alter the contrast between tissues from that normally achieved independently from the spin-echo or gradient-echo portion of the scan.
  • a method determines a radio frequency (RF) pulse sequence of N RF pulses and N-l interpulse interval(s) for use in magnetic resonance imaging (MRI) of at least a portion of a subject comprising two chemical species, such as water and fat for example, having a chemical shift difference in resonant frequency.
  • the number N of RF pulses is an integer greater than one and may be greater than or equal to three, for example.
  • a numerical optimization is performed to determine an amplitude and phase angle for each of the N RF pulses and a duration for each of the N-l interpulse interval(s) so as to excite magnetization of a selective one of the two chemical species for MRI detection upon application of the RF pulse sequence to at least a portion of the subject.
  • a total duration of the RF pulse sequence may be constrained in performing the optimization.
  • the optimization may be performed so as to help minimize magnetization of the selective one of the two chemical species along a predetermined axis and help maximize magnetization of the other one of the two chemical species along the predetermined axis upon application of the RF pulse sequence to at least a portion of the subject while constraining the total duration of the RF pulse sequence.
  • the optimization may also be performed so as to help minimize a total duration of the RF pulse sequence while constraining magnetization excitation of the selective one of the two chemical species for MRI detection upon application of the RF pulse sequence to at least a portion of the subject.
  • the optimization may be performed so as to help minimize total interpulse interval time while constraining magnetization excitation of the selective one of the two chemical species for MRI detection upon application of the RF pulse sequence to at least a portion of the subject. Magnetization of each of the two chemical species along a predetermined axis may be constrained in performing the optimization.
  • the optimization may further constrain total interpulse interval time, the duration of each interpulse interval, the phase angle for each RF pulse, and/or a magnetization tip angle to be effectuated by each RF pulse upon application to at least a portion of the subject.
  • the determined RF pulse sequence may be applied to at least a portion of the subject, and an image may be reconstructed from resulting RF magnetic resonance (MR) signals detected from at least a portion of the subject.
  • MR magnetic resonance
  • a magnetic resonance imaging (MRI) system comprises a static magnet, pulse sequence apparatus, pulse sequence control apparatus, and a computer system.
  • the static magnet produces a magnetic field along a predetermined axis relative to at least a portion of the subject in an examination region.
  • the magnetic field may be approximately 0.2 Tesla, for example.
  • the pulse sequence apparatus creates magnetic field gradients in the examination region, applies radio frequency (RF) pulsed magnetic fields in the examination region, and receives RF magnetic resonance (MR) signals from the examination region.
  • the pulse sequence control apparatus controls the pulse sequence apparatus to apply an RF pulse sequence in the examination region so as to excite magnetization of a selective one of the two chemical species.
  • the RF pulse sequence is determined in accordance with the numerical optimization which may be performed by the computer system.
  • the computer system reconstructs an image from received RF MR signals resulting from application of the RF pulse sequence in the examination region.
  • Figures 1 A, IB, IC, ID, and IE illustrate in graph form water and fat magnetization subjected to a prior art binomial l-(-l) RF pulse sequence for fat suppression;
  • Figures 2A, 2B, and 2C illustrate in graph form water and fat magnetization subjected to a prior art inversion recovery RF pulse sequence for fat suppression
  • FIG. 3 illustrates in block diagram form an exemplary magnetic resonance imaging (MRI) system for performing optimized chemical-shift excitation in accordance with the present invention
  • Figures 4A, 4B, 4C, 4D, 4E, and 4F illustrate in graph form water and fat magnetization subjected to an exemplary binomial-like RF pulse sequence for water excitation in accordance with the present invention.
  • a magnetic resonance imaging (MRI) system performs optimized chemical-shift excitation.
  • a computer system performs a numerical optimization for the MRI system to determine a set of parameters including radio frequency (RF) pulse amplitudes or strengths, RF pulse phase angles, and interpulse intervals for a binomial-like RF pulse sequence of N RF pulses that will excite a desired nuclear or chemical species, such as water for example.
  • RF radio frequency
  • the optimization performed by the computer system may constrain and/or help minimize the total interpulse interval time to ensure the resulting binomial-like RF pulse sequence requires relatively less time and to help minimize Tl and/or T2 relaxation.
  • EXEMPLARY MAGNETIC RESONANCE IMAGING (MRI) SYSTEM Figure 3 illustrates an exemplary magnetic resonance imaging (MRI) system 100 for performing optimized chemical-shift excitation in accordance with the present invention.
  • MRI system 100 The operation of MRI system 100 is controlled by a computer system 110.
  • a console 120 comprising a control panel 122 and a display 124 communicates with computer system 110 to enable an operator to control the production and display of MRI images on display 124.
  • a static magnet 132 produces a substantially uniform, temporally constant magnetic field along a desired z-axis such that selected nuclear magnetic dipoles of subject 102 within examination region 104 preferentially align with the magnetic field.
  • subject 102 may be an animal subject or any other suitable sample.
  • Computer system 110 communicates with a pulse program generator 142 to control a set of G x , G y , G z gradient amplifiers and coils 134, a radio frequency (RF) transmitter 152, and an RF receiver 154 so as to carry out a desired MRI scan sequence.
  • RF transmitter 152 transmits RF pulses into examination region 104 using RF coils 156 to cause magnetic resonance of the preferentially aligned dipoles of subject 102 within examination region 104.
  • RF receiver 154 receives RF magnetic resonance (MR) signals detected by RF coils 156 from the resonating dipoles of examination region 104.
  • MR magnetic resonance
  • Pulse program generator 142 also controls a transmit/receive (T/R) switch 158 selectively connecting RF transmitter 152 and RF receiver 154 to RF coils 156. Separate transmit and receive RF coils may also be used, obviating any need for T/R switch 158.
  • Computer system 110 comprises an analog-to-digital converter 144 to receive the RF MR signals from RF receiver 154 in digital form and processes the digitized RF MR signals to reconstruct an image representation for display on display 124.
  • Gradient amplifiers and coils 134 impose time- varying magnetic field gradients with the static magnetic field along mutually orthogonal x, y, z-axes to spatially encode the received RF MR signals. In this manner, images may be scanned along a particular one of contiguous parallel slice-volumes p, q, ..., z defined in examination region 104.
  • Computer system 110 loads software or program code defining different MRI pulse sequences into writable control storage areas of pulse program generator 142.
  • Pulse program generator 142 executes program code corresponding to a given pulse sequence to provide suitable signals that control the operation of RF transmitter 152, RF receiver 154, T/R switch 158, and gradient amplifiers and coils 134 and thereby effectuate the given pulse sequence.
  • Computer system 110 can specify and effectuate any suitable MRI pulse sequence for MRI system 100 as desired.
  • computer system 110 performs a numerical optimization to determine a set of parameters including RF pulse amplitudes or strengths, RF pulse phase angles, and interpulse intervals for a binomial-like RF pulse sequence of N RF pulses that will excite a desired chemical species, such as water for example, of at least a portion of subject 102.
  • the number N of RF pulses is an integer greater than one and may be two, three, or four, for example.
  • the present invention may be used for selective excitation of any other suitable chemical species having a chemical shift difference in resonance frequency.
  • the numerical optimization problem for one embodiment is formulated as the product of a series of rotation/transformation matrices.
  • the xyz magnetization for water and fat of subject 102 is described as:
  • Equation 1 where M x , M y , and M z represent magnetization along the x, y, and z axes, respectively.
  • a RF pulse rotation matrix is described as:
  • Equation 2 where ⁇ curriculum is the angle at which the nth RF pulse of the binomial-like RF pulse sequence is to tip the water and fat magnetization.
  • Equation 3 where ⁇ n is the duration of the nth interpulse interval of the binomial-like RF pulse sequence and k is a constant that relates interpulse interval time to a dephasing angle between fat and water.
  • ⁇ n is the phase angle of the nth RF pulse of the binomial-like RF pulse sequence.
  • ⁇ is a rotation matrix used to express the current Mxyin terms of components parallel and perpendicular to the phase modulated RF pulse.
  • the first RF pulse phase angle ⁇ is set to 0° while the remaining phase angles ⁇ personally for all subsequent RF pulses of the binomial-like RF pulse sequence are set relative to this first phase angle ⁇ i.
  • ⁇ fo) R( ⁇ 3 ) ⁇ t ⁇ 3 )P( ⁇ 2 ) ⁇ - I t ⁇ 2 )R( ⁇ 2 ) ⁇ ( % )R( ⁇ 1 )R( ⁇ 1 )
  • computer system 110 determines an optimal or near-optimal set of RF pulse tip angles ⁇ n , interpulse intervals ⁇ n , and RF pulse phase angles ⁇ n for a binomial-like RF pulse sequence of N RF pulses that will tip water magnetization into the detection plane and restore fat magnetization to the longitudinal axis.
  • Computer system 110 for one embodiment attempts to minimize the water magnetization M z water along the z-axis and maximize the fat magnetization M z at along the z-axis in determining the set of parameters for a binomial-like RF pulse sequence of N RF pulses.
  • the function f is the squared deviation from the condition when the water magnetization along the z-axis is zero, indicating all water magnetization is in the transverse plane, and when the fat magnetization along the z-axis is one, indicating all fat magnetization is restored along the z-axis.
  • the optimization performed by computer system 110 for one embodiment constrains the total sequence time in determining the set of parameters to ensure the resulting binomial-like RF pulse sequence requires relatively less time.
  • the total sequence time may be constrained, for example, by constraining the duration of each interpulse interval within a predetermined time range and the total interpulse interval time within a predetermined time range as follows.
  • the minimum allowable interpulse interval ⁇ n for a binomiallike RF pulse sequence is Xmin
  • the maximum allowable interpulse interval ⁇ n for a binomial-like RF pulse sequence is t m a .
  • the minimum and maximum interpulse interval times ⁇ m in and ⁇ max may be set to any suitable value.
  • each interpulse interval ⁇ n is measured from the centers of the nth and (n+l)th RF pulses
  • the minimum allowable total inte ⁇ ulse interval time ⁇ n for a binomial-like RF pulse sequence is TTmi n
  • the maximum allowable total inte ⁇ ulse interval time ⁇ n for a binomial-like RF pulse sequence is TT m ax-
  • the minimum and maximum total inte ⁇ ulse interval times TTmin and TT m a x may be set to any suitable value.
  • each inte ⁇ ulse interval ⁇ n is measured from the centers of the nth and (n+l)th RF pulses
  • the minimum total inte ⁇ ulse interval time TT m in may be set to (N-1)*T, and the maximum total inte ⁇ ulse interval time TT m x may be set to any suitable greater value.
  • the maximum total inte ⁇ ulse interval time TTmax may be set such that ⁇ n is less than the duration of the inte ⁇ ulse interval for a single dephasing in typical binomial methods, or k* ⁇ n ⁇ 180°.
  • the optimization performed by computer system 110 may also constrain the values for the RF pulse tip angles ⁇ n and RF pulse phase angles ⁇ n as follows.
  • the minimum allowable RF pulse tip angle ⁇ n is ⁇ m in, and the maximum allowable RF pulse tip angle ⁇ n is ⁇ ma .
  • the minimum and maximum RF pulse tip angles ⁇ min and ⁇ max may be set to any suitable value.
  • the minimum allowable RF pulse phase angle ⁇ n is ⁇ m i n
  • the maximum allowable RF pulse phase angle ⁇ n is q .
  • the minimum and maximum RF pulse phase angles ⁇ m i n and ⁇ max may be set to any suitable value.
  • the minimum RF pulse tip angle ⁇ min may be set to 0°
  • the maximum RF pulse tip angle ⁇ max may be set to 180°
  • the minimum RF pulse phase angle ⁇ min may be set to -180°
  • the maximum RF pulse phase angle c m a x may be set to 180° so that the RF pulses for a binomial-like RF pulse sequence may perform any possible rotation of the water and fat magnetization.
  • Computer system 110 for another embodiment attempts to minimize the total inte ⁇ ulse interval times as follows:
  • Equation 10 in determining the set of parameters for a binomial-like RF pulse sequence of N RF pulses.
  • This optimization performed by computer system 110 may constrain the final water magnetization M z ater along the z-axis to a value less than or equal to a predetermined amount Kl and/or the final fat magnetization M z fat along the z-axis to a value greater than or equal to a predetermined amount K2 as follows.
  • M ⁇ ⁇ Kl Kl and K2 may each have any suitable value.
  • Kl may be approximately 0.05, for example, and K2 may be approximately 0.95, for example.
  • Computer system 110 may attempt to minimize the total inte ⁇ ulse interval time in this manner to better ensure minimal Tl and or T2 relaxation.
  • computer system 110 may use one or more of the constraints C1-C4 in attempting to minimize the total inte ⁇ ulse interval time for a binomial-like RF pulse sequence.
  • Computer system 110 may perform the optimizations for equations 9 and 10 and constraints C1-C6 using any suitable nonlinearly constrained optimization algorithm.
  • Computer system 110 for one embodiment may use the nonlinearly constrained optimization algorithm in the Optimization Toolbox of the Matlab 5.2 programming environment provided by The Mathworks of Nattick, MA.
  • computer system 110 may then control MRI system 100 to apply the binomial-like RF pulse sequence to subject 102.
  • Computer system 110 may load suitable program code defining the binomial-like RF pulse sequence into pulse program generator 142.
  • Pulse program generator 142 may then execute the program code to thereby effectuate the binomial-like RF pulse sequence.
  • any suitable computer system such as a personal computer for example, may be used to determine the set of parameters for a binomial-like RF pulse sequence.
  • the determined set of parameters may then be programmed or entered into computer system 110 in a suitable manner using console 120, for example.
  • the second RF pulse characterized by a tip angle of ⁇ 2 ° and a phase angle of ⁇ 2°, tips both water magnetization 41 and fat magnetization 42 by ⁇ 2 ° as illustrated in Figure 4D.
  • water magnetization 41 and fat magnetization 42 precess (k*T2)° out of phase from their relative position following the second RF pulse, as illustrated in Figure 4E.
  • the third RF pulse characterized by a tip angle of ⁇ 3 ° and a phase angle of ⁇ 3 °, tips both water magnetization 41 and fat magnetization 42 by ⁇ 3 ° such that water magnetization 41 is tipped into the detection plane and fat magnetization 42 is restored to the z-axis as illustrated in Figure 4F.
  • MRI system 100 may apply binomial-like RF pulse sequences at any suitable magnetic field B 0 .
  • a binomial-like RF pulse sequence may be determined so as to require relatively less time with minimal Tl and/or T2 relaxation as compared to typical binomial or inversion recovery sequences
  • MRI system 100 may allow the scan TR and hence scan time to increase or may reduce the number of slices in examination region 104 in interleaved multi-slice experiments while maintaining TR substantially constant.
  • any suitable MRI system may be used.
  • One suitable MRI system is a Siemens Magnetom Open ® 0.2T resistive imager, manufactured by Siemens Medical Systems of Erlangen, Germany, with Numaris V3.5.1 software, a 26ms/500ms spin-echo sequence, and a
  • computer system 110 may also determine binomial-like RF pulse sequences to suppress fat magnetization.
  • Computer system 110 may similarly determine the set of parameters for a binomial-like RF pulse sequence that will tip fat magnetization into the detection plane and restore water magnetization to the longitudinal axis so that the fat magnetization may be spoiled as described in connection with Figure IE. The water magnetization may then be tipped into the detection plane by a selective RF pulse.

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  • Physics & Mathematics (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Abstract

Un système (100) d'imagerie par résonance magnétique (IRM) effectue une excitation optimisée du déplacement chimique. Un système informatique (110) effectue une optimisation numérique contrainte afin de déterminer les amplitudes d'impulsions de fréquence radio (RF), les angles de phase et les intervalles inter-impulsions pour une séquence d'impulsions RF de type binomial qui vont exciter la magnétisation (41) de l'une de deux espèces chimiques sélectives, telle que par exemple de l'eau et de la graisse, d'un sujet (102) en relativement moins de temps et que l'on peut par conséquent utiliser à des champs magnétiques inférieurs. Un aimant statique (132) produit un champ magnétique le long d'un axe prédéterminé par rapport au sujet. Un appareil (134, 152, 154, 156, 158) à séquences d'impulsions crée des gradients de champ magnétique avec le champ magnétique, il applique des champs magnétiques pulsés RF et il reçoit des signaux de résonance magnétique (RM, RF) résultants. Un appareil (142) de commande de séquences d'impulsions commande l'appareil à séquences d'impulsions afin d'appliquer la séquence d'impulsions RF de type binomial au sujet. Le système informatique reconstruit une image à partir des signaux RF RM reçus résultant de l'application de la séquence d'impulsions RF de type binomial.
PCT/US1998/020100 1997-09-26 1998-09-25 Excitation optimisee du deplacement chimique en imagerie par resonance magnetique (irm) WO1999015915A1 (fr)

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US09/509,325 US6404198B1 (en) 1997-09-26 1998-09-25 Magnetic resonance imaging (MRI) optimized chemical-shift excitation
AU96665/98A AU9666598A (en) 1997-09-26 1998-09-25 Magnetic resonance imaging (mri) optimized chemical-shift excitation

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US6018497P 1997-09-26 1997-09-26
US60/060,184 1997-09-26

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US20030210044A1 (en) * 2002-05-13 2003-11-13 Ken-Pin Hwang Missing pulse steady state free precession
DE10314407A1 (de) * 2003-03-28 2004-11-04 Siemens Ag Hybrid-CSI-Verfahren
WO2006046450A1 (fr) * 2004-10-29 2006-05-04 Hitachi Medical Corporation Dispositif d'imagerie par résonance magnétique
US20070282318A1 (en) * 2006-05-16 2007-12-06 Spooner Gregory J Subcutaneous thermolipolysis using radiofrequency energy
EP2399142B1 (fr) * 2009-02-18 2014-06-11 Commissariat à l'Énergie Atomique et aux Énergies Alternatives Utilisation d'impulsions à forte modulation en irm pour obtenir des angles de bascule sélectifs des déplacements chimiques
US8749234B2 (en) * 2011-01-28 2014-06-10 General Electric Company Method and system for designing excitation pulses for magnetic resonance imaging
US8248070B1 (en) * 2011-03-22 2012-08-21 Kabushiki Kaisha Toshiba MRI using prep scan sequence producing phase-offset NMR signals from different NMR species

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10578695B2 (en) 2016-04-18 2020-03-03 Centre Hospitalier Universitaire Vaudois Differentiated tissue excitation in MRI

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